Aluminum layers are used in flat panel display screens to reflect photons back to the viewer. In conventional flat panel display devices, a black border or "black matrix" has also been used to achieve improved display characteristics. Typically, the black matrix is formed on the inside of the viewing screen panel opposite the viewing side of the screen and is comprised of organic materials.
The black matrix is comprised of raised borders, which surround and define a plurality of wells. In a typical flat panel display, phosphors are deposited into these wells. The phosphors give off light when bombarded by electrons. These phosphors convert the electron energy into visible light to form an image on the viewing screen. Each well contains a color "sub-pixel" of red, blue, or green light-emitting phosphors. By segregating color sub-pixels, the black matrix increases the contrast of the display by keeping the colors cleanly separated.
As stated above, light is generated by phosphors when beams of electrons excite the phosphors disposed in the wells of the black matrix. Light generated in this manner is emitted in the direction of the viewing screen to be seen by the viewer. However, some light is emitted in the opposite direction away from the viewing screen. To redirect or reflect this light towards the viewing screen, an aluminum layer is disposed on top of the phosphor layer. Unfortunately, conventional aluminum layers have several shortcomings associated therewith. These shortcomings originate from limitations in fabrication processes and temperature limitations of materials associated with aluminum layer creation steps. Schematic side sectional views depicting conventional steps used in fabricating an aluminum layer are shown in Prior Art FIGS. 1A through 1F.
With reference to Prior Art FIG. 1A, a side sectional view of a raised black matrix 100 having orthogonally arranged portions 102 and 104 is shown. Black matrix 100 is disposed on the interior surface of a viewing screen. As shown in Prior Art FIG. 1A, orthogonally arranged portions 102 and 104 of black matrix 100 define wells there between.
Referring now to Prior Art FIG. 1B, phosphors, typically shown as 106, are deposited into the wells defined by orthogonally arranged portions 102 and 104 of black matrix 100.
Next, referring to Prior Art FIG. 1C, a lacquer layer 108 is deposited on top of phosphors 106. Lacquer layer 108 is used to form a relatively flat surface on top of phosphors 106. However as shown in FIG. 1C, lacquer layer 108 is conformal. As a result, lacquer layer 108 is non-planar. That is, lacquer layer 108 has a surface topography which very closely resembles the surface shape of phosphors 106 residing directly beneath lacquer layer 108.
As shown in Prior Art FIG. 1D, an aluminum layer 110 is then deposited on top of lacquer layer 108. As with conformal lacquer layer 108, aluminum layer 110 conforms to the shape of the underlying topography. As a result, aluminum layer 110 has substantially the same shape as lacquer layer 108, and the surface shape of underlying phosphors 106. Thus, aluminum layer 110 has a substantially non-planar topography.
In reference to Prior Art FIG. 1E, aluminum layer 110 is shown after baking off lacquer layer 108. Lacquer layer 108 has been evaporated through tiny pores in aluminum layer 110, leaving only aluminum layer 110 disposed on top of phosphors 106. Even after the baking out process, the surface of aluminum layer 110 remains non-planar. That is, the surface of aluminum layer 110 still conforms to the shape of the surface of phosphors 106.
Prior Art FIG. 1F depicts several paths of light 112 generated by phosphors 106. As shown in Prior Art FIG. 1F, light 112 is emitted from phosphors 106 in the direction of aluminum layer 110. Due to the non-planar surface of aluminum layer 110, light 112 may scatter in other directions, instead of being redirected or reflected towards the viewing screen. As yet another drawback associated with a non-planar aluminum layer, electrons may be deflected away from the phosphors. As a result, the non-planar aluminum layer acts as a barrier to some of the electrons emitted from electron emitting devices, thereby further reducing the efficiency of the flat panel display. Therefore, the efficiency of the flat panel display is decreased due to the loss of light 112 through aluminum layer 110 and the impedance of electrons by aluminum layer 110.
In one attempt to obtain a planar layer of aluminum, the depth of prior art aluminum layer 110 has been increased. However, such an aluminum layer with an increased thickness can reduce the efficiency of the flat panel displays by preventing electrons from penetrating the thickened aluminum layer. As a result, emitted electrons never reach their intended target, the phosphors. Hence, less light is generated in such thick aluminum layer embodiments.
Additionally, conventional aluminum layer fabrication methods are severely limited by the temperature limitations of black matrix material, aluminum, and phosphors. More specifically, the black matrix is made up of organic materials which cannot withstand temperatures over 380 degrees Celsius. Above this temperature, the black matrix undergoes pyrolysis with resulting damages to its internal organic structure. Hence, prior art bake off processes are limited to 380 degrees Celsius or lower. Such temperature limitation in turn limits the lacquer materials which can be used in the process. That is, acceptable lacquers are limited only to those having relatively light solid contents and/or molecular weight species such as, for example, nitrocellulose. Unfortunately, light solid contents and/or molecular weight species tend to conform to the surface of phosphors. Thus, these lacquers do not produce a smooth planar surface on top of the phosphors.
On the other hand, lacquers containing higher solid content and/or molecular weight species such as acrylics would produce a more smooth planar surface. However, these lacquers do not burn out cleanly at temperatures of 380 degrees Celsius or lower. This temperature limitation has prevented wide use of lacquers with higher solid content and/or molecular weight species.
Furthermore, even if the black matrix or the lacquer layer could tolerate temperatures higher than 380 degrees Celsius, such temperatures would have a deleterious effect on other materials, such as, for example aluminum and phosphors. Under such higher temperatures, unwanted oxidation of the aluminum and phosphors may occur. This oxidation may cause the aluminum layer to lose its characteristic reflectivity. Similarly, phosphors can lose its characteristic efficiency. Therefore, higher temperatures have had an effect of reducing the efficiency of the flat panel display.
Thus, a need exists for a method to create a planar aluminum layer in a flat panel display structure which allows more light reflection toward the viewing screen. A further need exists to achieve the above-mentioned planar aluminum layer in a way which does not induce pyrolysis or otherwise damage a proximately located black matrix. Yet another need exists to achieve the planar aluminum layer without employing processes and/or temperatures which damage aluminum layer and the underlying phosphors, or impede the passage of emitted electrons through the aluminum layer.